Coastal or offshore structures such as pipelines installed on the seabed are submitted to cyclic horizontal loads either by the direct hydrodynamic wave action or through the cyclic movement of risers or flow lines transmitted by floating structures. In fine sandy or silty soils the cyclic loads can induce a liquefaction of the surrounding bed which can play an important part in the processes of erosion, trenching or self-burial of the pipes. A large 1g physical model was built to study the fluid-soil-structure interaction with special emphasis on the conditions of occurrence of liquefaction around a pipe instrumented with pore pressure sensors. The experiments indicate a strong increase in pore pressure at the pipe-soil interface and a lateral visualisation put into evidence the liquefaction of a soil band in the vicinity of the pipe.
The process of self burial of structures resting on the seabed induced by the wave action has been extensively studied by Lyons (1973), Lambrakos (1985), Brennoden et al (1986), Wagner et al (1987), Palmer et al (1988), Morris et al (1988), among others. Many of these studies were devoted to the specific pipe-soil interaction in order to elaborate design criteria for pipeline stability. A first experimental program was conducted at the University of Grenoble by Branque et al (2002) to quantify the influence of the cyclic amplitude and the density of the sand on the penetration of the pipe and the evolution of the lateral resistance. A transitory liquefaction of the soil close to the pipe could be noted for some of the tests, with peak cyclic pore pressures reaching the effective overburden stress. In the recent years, an increasing attention has been given to the effect of wave-induced liquefaction on the stability of coastal or offshore structures, in combination with scour effects.